Britain cannot have access to the economic single market without allowing the free movement of people, said French President Francois Hollande.
Of the four freedoms that make up the EU - goods, capital, services and people - Hollande said firmly "none can be separated from the other".
He spoke at a press conference in Paris with Britain's new Prime Minister Theresa May.
His assurance that it would simply not be possible to have single market access without the free movement of people will continue to be an issue in British politics - it is not yet clear the type of relationship Britain will opt for with the EU.
Brexiteers have disagreed over which is more important for the UK - single market access or control over immigration.
Hollande and May also clashed over the timings of Brexit.
Despite murmurings from European leaders that Brexit must happen as soon as possible, May repeated that she would not invoke Article 50 before the end of this year.
Though Hollande recognised the UK has the right to invoke Article 50 when it chooses, he expressed his wish that the UK withdraw quickly in order to reduce uncertainty in the markets.
There was friendly agreement between the pair on other issues though - border controls in Calais will remain in place, and Britain and France will remain firm allies.